Thermoresponsive hydrogel containing polymer microparticles for noninvasive ocular drug delivery

ABSTRACT

A method for sustained delivery of an agent to an ocular organ in a subject, comprising topically delivering to the ocular surface a liquid thermoresponsive hydrogel comprising agent-loaded polymer microparticles, wherein the agent is sustainably released for a period of at least five days.

PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No.14/772,758, filed Sep. 3, 2015, which is a § 371 National Phase of PCTApplication No. PCT/US2014/020355, filed Mar. 4, 2014, which claimspriority to and the benefit of U.S. Patent Application No. 61/773,076,filed Mar. 5, 2013, all of which are incorporated by reference in theirentirety.

BACKGROUND

It is estimated that nearly 4 million adults will be diagnosed with openangle glaucoma by the year 2020, the majority of which will be treatedwith a daily regimen of ocular hypotensive medication (Friedman et al.,2004). These IOP-reducing drugs are given as eye drops, which must beadministered frequently by the patient to reduce the risk ofirreversible vision loss. The rigorous dosing schedule, initial lack ofsymptoms, and difficult drop administration lead to extremely lowpatient compliance rates (Hermann et al., 2010). Additionally, eye dropadministration requires high concentrations of drug to overcome the manyabsorption barriers in the eye (Ghate and Edelhauser, 2008).

One of the main risk factors for glaucoma, the second leading cause ofblindness worldwide, is sustained ocular hypertension. Intraocularpressure (IOP) reduction in glaucoma patients is typically accomplishedthrough the administration of eye drops several times daily, thedifficult and frequent nature of which contributes to compliance ratesas low as 50%. Brimonidine tartrate (BT), a common glaucoma medicationwhich requires dosing every 8-12 hours, has yet to be adapted into acontrolled-release formulation that could drastically improvecompliance.

SUMMARY

One embodiment disclosed herein is a method for sustained delivery of anagent to an ocular organ in a subject, comprising topically deliveringto the ocular surface a liquid thermoresponsive hydrogel comprisingagent-loaded polymer microparticles, wherein the agent is sustainablyreleased for a period of at least five days.

A further embodiment disclosed herein is a method for ocular delivery ofan agent comprising administering the agent at the lower fornix of aneye in a subject, wherein the method comprises topically delivering toan eye a liquid hydrogel comprising agent-loaded polymer microparticles,and permitting the liquid hydrogel to form in situ a gelled, sustainedrelease structure residing in the lower fornix of the eye.

Also disclosed herein is a composition comprising agent-loaded polymermicroparticles dispersed within a thermoresponsive hydrogel, wherein theagent is an agent for treating an ocular condition and the compositionis configured for sustained topical ocular release of the agent.

Additionally disclosed herein is a drug depot positioned in the lowerfornix of an eye of a subject, wherein the drug depot comprises a gelledhydrogel comprising drug-loaded polymer microparticles.

The foregoing will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: SEM images of brimonidine tartrate-loaded PLGA microparticles(BTMPs). These images confirm the desired size and morphology of theBTMPs, consistent with volume impedance measurements (average volumediameter=7.46±2.86 μm).

FIG. 2: In vitro release of brimonidinefrom PLGA MPs (n=3). Also shownare the theoretical maximum and minimum amounts of brimonidine absorbed,based on 2 drops per day of 0.2% BT solution and 1-7% absorption (Ghateand Edelhauser, 2008) as well as 0.66 mg brimonidine per mg BT.

FIG. 3: BTMP bleb in subconjunctival space of Dutch belted rabbit on Day1 of study.

FIGS. 4A and 4B: Actual IOP measurements in each of the three groupstaken from FIG. 4A) the right eye (treated eye) and FIG. 4B) the lefteye (untreated eye). N=3 for BTMP and topical BT groups; n=2 for blankMP group.

FIGS. 5A and 5B: Delta IOP values (baseline minus current day) for eachof the three groups in FIG. 5A) the right eye (treated eye) and FIG. 5B)the left eye (untreated eye). N=3 for BTMP and topical BT groups; n=2for blank MP group.

FIG. 6: Partially degraded BTMPs in the subconjunctival space (stainedwith Masson's trichrome) following sacrifice on Day 28 of the study.

FIGS. 7A, 7B and 7C: A representation of an embodiment for administeringan embodiment of the microparticle/hydrogel delivery system disclosedherein.

FIG. 8: Agent release is not affected when microparticles are loadedinto hydrogel. Inset: SEM of hydrogel containing BT-loadedmicroparticles (scale bar=10 μm).

FIG. 9: Theoretical and actual release of Gd-DOTA and brimonidine frompolymer microparticles (brimonidine release data from FIGS. 2 and 8 withy-axis modified to represent % of total release).

FIGS. 10A and 10B: Whole brain T1-weighted MR images of NZW at 24 hafter intravitreal injection of thermoresponsive gel containing FIG.10A) Gd-DOTA-loaded MPs and FIG. 10B) soluble Gd-DOTA only. Injectionswere in the right eye only; scans performed within 1 h of sacrifice.

FIG. 11: A photo image of surgical resection of rabbit nictatingmembrane prior to drop administration.

FIGS. 12A and 12B: A photo image showing gel/microparticle dropadministration (FIG. 12A). No restraint or sedation was used during thistime for any of the rabbits. The presence of the gel drop in theinferior fornix was visually confirmed immediately followinginstillation (FIG. 12 B).

FIG. 13: Photo images showing the presence of gel/microparticle drop ininferior fornix from days 7-28. Note that visibility of the gels wasgreatly decreased from Day 21-28. Gels were stained with fluorescein toconfirm presence.

FIGS. 14A and 14B: Intraocular pressure data for BT drops (positivecontrol), BT-loaded microparticles (BTMP, prior experimental treatment),gel/BTMP (GelMP, current experimental treatment), and blankmicroparticles (blank MP, negative control). These results were reportedfor the treated eye (FIG. 14A) and the untreated contralateral eye (FIG.14B). The legend indicating statistic significance applies to both FIG.14A and FIG. 14B.

DETAILED DESCRIPTION Terminology

The following explanations of terms and methods are provided to betterdescribe the present compounds, compositions and methods, and to guidethose of ordinary skill in the art in the practice of the presentdisclosure. It is also to be understood that the terminology used in thedisclosure is for the purpose of describing particular embodiments andexamples only and is not intended to be limiting.

An “animal” refers to living multi-cellular vertebrate organisms, acategory that includes, for example, mammals and birds. The term mammalincludes both human and non-human mammals. Similarly, the term “subject”includes both human and non-human subjects, including birds andnon-human mammals, such as non-human primates, companion animals (suchas dogs and cats), livestock (such as pigs, sheep, cows), as well asnon-domesticated animals, such as the big cats.

The term “co-administration” or “co-administering” refers toadministration of a an agent disclosed herein with at least one othertherapeutic or diagnostic agent within the same general time period, anddoes not require administration at the same exact moment in time(although co-administration is inclusive of administering at the sameexact moment in time). Thus, co-administration may be on the same day oron different days, or in the same week or in different weeks. In certainembodiments, a plurality of therapeutic and/or diagnostic agents may beco-administered by encapsulating the agents within the microparticlesdisclosed herein.

“Inhibiting” refers to inhibiting the full development of a disease orcondition. “Inhibiting” also refers to any quantitative or qualitativereduction in biological activity or binding, relative to a control.

“Microparticle”, as used herein, unless otherwise specified, generallyrefers to a particle of a relatively small size, but not necessarily inthe micron size range; the term is used in reference to particles ofsizes that can be, for example, administered to the eye in the form ofan eye drop that can be delivered from a squeeze nozzle container, andthus can be less than 50 nm to 100 microns or greater. In certainembodiments, microparticles specifically refers to particles having adiameter from about 1 to about 25 microns, preferably from about 10 toabout 25 microns, more preferably from about 10 to about 20 microns. Inone embodiment, the particles have a diameter from about 1 to about 10microns, preferably from about 1 to about 5 microns, more preferablyfrom about 2 to about 5 microns. As used herein, the microparticleencompasses microspheres, microcapsules and microparticles, unlessspecified otherwise. A microparticle may be of composite constructionand is not necessarily a pure substance; it may be spherical or anyother shape.

“Ocular region” or “ocular site” means any area of the eye, includingthe anterior and posterior segment of the eye, and which generallyincludes, but is not limited to, any functional (e.g., for vision) orstructural tissues found in the eyeball, or tissues or cellular layersthat partly or completely line the interior or exterior of the eyeball.Ocular regions include the anterior chamber, the posterior chamber, thevitreous cavity, the choroid, the suprachoroidal space, the subretinalspace, the conjunctiva, the subconjunctival space, the episcleral space,the intracorneal space, the epicorneal space, the sclera, the parsplana, surgically-induced avascular regions, the macula, and the retina.

“Ocular condition” means a disease, ailment or condition which affectsor involves the eye or one of the parts or regions of the eye. Broadlyspeaking the eye includes the eyeball and the tissues and fluids whichconstitute the eyeball, the periocular muscles (such as the oblique andrectus muscles) and the portion of the optic nerve which is within oradjacent to the eyeball.

A “therapeutically effective amount” refers to a quantity of a specifiedagent sufficient to achieve a desired effect in a subject being treatedwith that agent. Ideally, a therapeutically effective amount of an agentis an amount sufficient to inhibit or treat the disease or conditionwithout causing a substantial cytotoxic effect in the subject. Thetherapeutically effective amount of an agent will be dependent on thesubject being treated, the severity of the affliction, and the manner ofadministration of the therapeutic composition. For example, a“therapeutically effective amount” may be a level or amount of agentneeded to treat an ocular condition, or reduce or prevent ocular injuryor damage without causing significant negative or adverse side effectsto the eye or a region of the eye

“Treatment” refers to a therapeutic intervention that ameliorates a signor symptom of a disease or pathological condition after it has begun todevelop, or administering a compound or composition to a subject whodoes not exhibit signs of a disease or exhibits only early signs for thepurpose of decreasing the risk of developing a pathology or condition,or diminishing the severity of a pathology or condition. As used herein,the term “ameliorating,” with reference to a disease or pathologicalcondition, refers to any observable beneficial effect of the treatment.The beneficial effect can be evidenced, for example, by a delayed onsetof clinical symptoms of the disease in a susceptible subject, areduction in severity of some or all clinical symptoms of the disease, aslower progression of the disease, an improvement in the overall healthor well-being of the subject, or by other parameters well known in theart that are specific to the particular disease. The phrase “treating adisease” refers to inhibiting the full development of a disease, forexample, in a subject who is at risk for a disease such as glaucoma.“Preventing” a disease or condition refers to prophylactic administeringa composition to a subject who does not exhibit signs of a disease orexhibits only early signs for the purpose of decreasing the risk ofdeveloping a pathology or condition, or diminishing the severity of apathology or condition. In certain embodiments, “treating” meansreduction or resolution or prevention of an ocular condition, ocularinjury or damage, or to promote healing of injured or damaged oculartissue

“Pharmaceutical compositions” are compositions that include an amount(for example, a unit dosage) of one or more of the disclosed compoundstogether with one or more non-toxic pharmaceutically acceptableadditives, including carriers, diluents, and/or adjuvants, andoptionally other biologically active ingredients. Such pharmaceuticalcompositions can be prepared by standard pharmaceutical formulationtechniques such as those disclosed in Remington's PharmaceuticalSciences, Mack Publishing Co., Easton, Pa. (19th Edition).

The terms “pharmaceutically acceptable salt or ester” refers to salts oresters prepared by conventional means that include salts, e.g., ofinorganic and organic acids, including but not limited to hydrochloricacid, hydrobromic acid, sulfuric acid, phosphoric acid, methanesulfonicacid, ethanesulfonic acid, malic acid, acetic acid, oxalic acid,tartaric acid, citric acid, lactic acid, fumaric acid, succinic acid,maleic acid, salicylic acid, benzoic acid, phenylacetic acid, mandelicacid and the like. “Pharmaceutically acceptable salts” of the presentlydisclosed compounds also include those formed from cations such assodium, potassium, aluminum, calcium, lithium, magnesium, zinc, and frombases such as ammonia, ethylenediamine, N-methyl-glutamine, lysine,arginine, ornithine, choline, N,N′-dibenzylethylenediamine,chloroprocaine, diethanolamine, procaine, N-benzylphenethylamine,diethylamine, piperazine, tris(hydroxymethyl)aminomethane, andtetramethylammonium hydroxide. These salts may be prepared by standardprocedures, for example by reacting the free acid with a suitableorganic or inorganic base. Any chemical compound recited in thisspecification may alternatively be administered as a pharmaceuticallyacceptable salt thereof. “Pharmaceutically acceptable salts” are alsoinclusive of the free acid, base, and zwitterionic forms. Descriptionsof suitable pharmaceutically acceptable salts can be found in Handbookof Pharmaceutical Salts, Properties, Selection and Use, Wiley VCH(2002). When compounds disclosed herein include an acidic function suchas a carboxy group, then suitable pharmaceutically acceptable cationpairs for the carboxy group are well known to those skilled in the artand include alkaline, alkaline earth, ammonium, quaternary ammoniumcations and the like. Such salts are known to those of skill in the art.For additional examples of “pharmacologically acceptable salts,” seeBerge et al., J. Pharm. Sci. 66:1 (1977).

“Pharmaceutically acceptable esters” includes those derived fromcompounds described herein that are modified to include a carboxylgroup. An in vivo hydrolysable ester is an ester, which is hydrolysed inthe human or animal body to produce the parent acid or alcohol.Representative esters thus include carboxylic acid esters in which thenon-carbonyl moiety of the carboxylic acid portion of the ester groupingis selected from straight or branched chain alkyl (for example, methyl,n-propyl, t-butyl, or n-butyl), cycloalkyl, alkoxyalkyl (for example,methoxymethyl), aralkyl (for example benzyl), aryloxyalkyl (for example,phenoxymethyl), aryl (for example, phenyl, optionally substituted by,for example, halogen, C.sub.1-4 alkyl, or C.sub.1-4 alkoxy) or amino);sulphonate esters, such as alkyl- or aralkylsulphonyl (for example,methanesulphonyl); or amino acid esters (for example, L-valyl orL-isoleucyl). A “pharmaceutically acceptable ester” also includesinorganic esters such as mono-, di-, or tri-phosphate esters. In suchesters, unless otherwise specified, any alkyl moiety presentadvantageously contains from 1 to 18 carbon atoms, particularly from 1to 6 carbon atoms, more particularly from 1 to 4 carbon atoms. Anycycloalkyl moiety present in such esters advantageously contains from 3to 6 carbon atoms. Any aryl moiety present in such esters advantageouslycomprises a phenyl group, optionally substituted as shown in thedefinition of carbocycylyl above. Pharmaceutically acceptable estersthus include C1-C22 fatty acid esters, such as acetyl, t-butyl or longchain straight or branched unsaturated or omega-6 monounsaturated fattyacids such as palmoyl, stearoyl and the like. Alternative aryl orheteroaryl esters include benzoyl, pyridylmethyloyl and the like any ofwhich may be substituted, as defined in carbocyclyl above. Additionalpharmaceutically acceptable esters include aliphatic L-amino acid esterssuch as leucyl, isoleucyl and especially valyl.

For therapeutic use, salts of the compounds are those wherein thecounter-ion is pharmaceutically acceptable. However, salts of acids andbases which are non-pharmaceutically acceptable may also find use, forexample, in the preparation or purification of a pharmaceuticallyacceptable compound.

The pharmaceutically acceptable acid and base addition salts asmentioned hereinabove are meant to comprise the therapeutically activenon-toxic acid and base addition salt forms which the compounds are ableto form. The pharmaceutically acceptable acid addition salts canconveniently be obtained by treating the base form with such appropriateacid. Appropriate acids comprise, for example, inorganic acids such ashydrohalic acids, e.g. hydrochloric or hydrobromic acid, sulfuric,nitric, phosphoric and the like acids; or organic acids such as, forexample, acetic, propanoic, hydroxyacetic, lactic, pyruvic, oxalic (i.e.ethanedioic), malonic, succinic (i.e. butanedioic acid), maleic,fumaric, malic (i.e. hydroxybutanedioic acid), tartaric, citric,methanesulfonic, ethanesulfonic, benzenesulfonic, p-toluenesulfonic,cyclamic, salicylic, p-aminosalicylic, pamoic and the like acids.Conversely said salt forms can be converted by treatment with anappropriate base into the free base form.

The compounds containing an acidic proton may also be converted intotheir non-toxic metal or amine addition salt forms by treatment withappropriate organic and inorganic bases. Appropriate base salt formscomprise, for example, the ammonium salts, the alkali and earth alkalinemetal salts, e.g. the lithium, sodium, potassium, magnesium, calciumsalts and the like, salts with organic bases, e.g. the benzathine,N-methyl-D-glucamine, hydrabamine salts, and salts with amino acids suchas, for example, arginine, lysine and the like.

The term “addition salt” as used hereinabove also comprises the solvateswhich the compounds described herein are able to form. Such solvates arefor example hydrates, alcoholates and the like.

The term “quaternary amine” as used hereinbefore defines the quaternaryammonium salts which the compounds are able to form by reaction betweena basic nitrogen of a compound and an appropriate quaternizing agent,such as, for example, an optionally substituted alkylhalide, arylhalideor arylalkylhalide, e.g. methyliodide or benzyliodide. Other reactantswith good leaving groups may also be used, such as alkyltrifluoromethanesulfonates, alkyl methanesulfonates, and alkylp-toluenesulfonates. A quaternary amine has a positively chargednitrogen. Pharmaceutically acceptable counterions include chloro, bromo,iodo, trifluoroacetate and acetate. The counterion of choice can beintroduced using ion exchange resins.

Delivery Systems

Disclosed herein are microparticle/hydrogel ocular delivery systems. Thedelivery systems disclosed herein are noninvasive since amicroparticle/hydrogel suspension can be self-administered to the lowerfornix and removed by the subject (e.g., with tweezers or a salinesolution). Current applications for microparticles or hydrogels forocular conditions require injection to the anterior chamber or vitreousby a clinician. In addition, the current clinical standard is topicaleye drop medication that lasts a few hours. In contrast, the presentlydisclosed systems could provide sustained delivery for at least onemonth.

The agent for inclusion in the delivery systems disclosed may be atherapeutic agent, a diagnostic agent, an imaging agent, a cosmeticagent, or other agents. In one embodiment, the one or more therapeuticagents are useful for treating ocular conditions. Suitable classes oftherapeutic agents include, but are not limited to, active agents thatlower intraocular pressure, antibiotics (including antibacterials andanitfungals), anti-inflammatory agents, chemotherapeutic agents, agentsthat promote nerve regeneration, steroids, immunosuppressants,neuroprotectants, dry eye syndrome treatment agents (e.g.,immunosuppressants, anti-inflammatory agents, steroids, comfort agentsuch as carboxymethyl cellulose), and combinations thereof. Thetherapeutic agents described above can be administered alone or incombination to treat ocular conditions.

In one embodiment, the microparticles contain one or more active agentsthat manage (e.g., reduce) elevated IOP in the eye. Suitable activeagents include, but are not limited to, prostaglandins analogs, such astravoprost, bimatoprost, latanoprost, unoprostine, and combinationsthereof; and carbonic anhydrase inhibitors (CAL), such as methazolamide,and 5-acylimino- and related imino-substituted analogs of methazolamide;and combinations thereof. The microparticles can be administered aloneor in combination with microparticles containing a second drug thatlowers IOP.

In a further embodiment, the agent may be a beta adrenergic receptorantagonist or an alpha adrenergic receptor agonist.

Illustrative beta adrenergic receptor antagonists include timolol,levobunalol, carteolol, metipranolol, betaxolol, or a pharmaceuticallyacceptable salt thereof, or combinations thereof. Illustrative alphaadrenergic receptor agonists include brimonidine, apraclonidine, or apharmaceutically acceptable salt thereof, or combinations thereof.Additional examples of anti-glaucoma agents include pilocarpine,epinephrine, dipivefrin, carbachol, acetazolamide, dorzolamide,brinzolamide, latanoprost, and bimatoprost.

The agent may be an antibiotic. Illustrative antibiotics include, butare not limited to, cephaloridine, cefamandole, cefamandole nafate,cefazolin, cefoxitin, cephacetrile sodium, cephalexin, cephaloglycin,cephalosporin C, cephalothin, cafcillin, cephamycins, cephapirin sodium,cephradine, penicillin BT, penicillin N, penicillin O, phenethicillinpotassium, pivampic ulin, amoxicillin, ampicillin, cefatoxin,cefotaxime, moxalactam, cefoperazone, cefsulodin, ceflizoxime,ceforanide, cefiaxone, ceftazidime, thienamycin, N-formimidoylthienamycin, clavulanic acid, penemcarboxylic acid, piperacillin,sulbactam, cyclosporine, moxifloxacin, vancomycin, and combinationsthereof.

The agent may be an inhibitor of a growth factor receptor. Suitableinhibitors include, but are not limited to, inhibitors of EpidermalGrowth Factor Receptor (EGFR), such as AG1478, and EGFR kinaseinhibitors, such as BIBW 2992, erlotinib, gefitinib, lapatinib, andvandetanib.

The agent may be a chemotherapeutic agent and/or a steroid. In oneembodiment, the chemotherapeutic agent is methotrexate. In anotherembodiment, the steroid is prednisolone acetate, triamcinolone,prednisolone, hydrocortisone, hydrocortisone acetate, hydrocortisonevalerate, vidarabine, fluorometholone, fluocinolone acetonide,triamcinolone acetonide, dexamethasone, dexamethasone acetate,loteprednol etabonate, prednisone, methylprednisone, betamethasone,beclometasone, fludrocortisone, deoxycorticosterone, aldosterone, andcombinations thereof.

Illustrative immunosuppressants include pimecrolimus, tacrolimus,sirolimus, cyclosporine, and combinations thereof.

In certain embodiments, the amount of agent loaded into themicroparticles may from 1 ng to 1 mg, more particularly 1 to 100 μg, andmost particularly, 20 to 30 μg agent per mg of microparticles. Incertain specific embodiments, the amount of agent loaded into themicroparticles is 25 30 μg agent per mg of microparticles.

The polymers for the microparticle may be bioerodible polymers so longas they are biocompatible. Preferred bio-erodible polymers arepolyhydroxyacids such as polylactic acid and copolymers thereof.Illustrative polymers include poly glycolide, poly lactic acid (PLA),and poly (lactic-co-glycolic acid) (PLGA). Another class of approvedbiodegradable polymers is the polyhydroxyalkanoates.

Other suitable polymers include, but are not limited to: polyamides,polycarbonates, polyalkylenes, polyalkylene glycols, polyalkyleneoxides, polyalkylene terephthalates, polyvinyl alcohols, polyvinylethers, polyvinyl esters, polyvinyl halides, polyvinylpyrrolidone,polyglycolides, polysiloxanes, polyurethanes and copolymers thereof,alkyl cellulose, hydroxyalkyl celluloses, cellulose ethers, celluloseesters, nitro celluloses, polymers of acrylic and methacrylic esters,methyl cellulose, ethyl cellulose, hydroxypropyl cellulose,hydroxy-propyl methyl cellulose, hydroxybutyl methyl cellulose,cellulose acetate, cellulose propionate, cellulose acetate butyrate,cellulose acetate phthalate, carboxylethyl cellulose, cellulosetriacetate, cellulose sulphate sodium salt, poly(methyl methacrylate),poly(ethylmethacrylate), poly(butylmethacrylate),poly(isobutylmethacrylate), poly(hexylmethacrylate),poly(isodecylmethacrylate), poly(lauryl methacrylate), poly(phenylmethacrylate), poly(methyl acrylate), poly(isopropyl acrylate),poly(isobutyl acrylate), poly(octadecyl acrylate), polyethylene,polypropylene polyethylene glycol), poly(ethylene oxide), poly(ethyleneterephthalate), poly(vinyl alcohols), poly(vinyl acetate), poly vinylchloride polystyrene, polyvinylpryrrolidone, alginate,poly(caprolactone), dextran and chitosan.

The percent loading of an agent may be increased by “matching” thehydrophilicity or hydrophobicity of the polymer to the agent to beencapsulated. In some cases, such as PLGA, this can be achieved byselecting the monomer ratios so that the copolymer is more hydrophilicfor hydrophilic drugs or less hydrophilic for hydrophobic drugs.Alternatively, the polymer can be made more hydrophilic, for example, byintroducing carboxyl groups onto the polymer. A combination of ahydrophilic drug and a hydrophobic drug can be encapsulated inmicroparticles prepared from a blend of a more hydrophilic PLGA and ahydrophobic polymer, such as PLA.

The preferred polymer is a PLGA copolymer or a blend of PLGA and PLA.The molecular weight of PLGA is from about 10 kD to about 80 kD, morepreferably from about 10 kD to about 35 kD. The molecular weight rangeof PLA is from about 20 to about 30 kDa. The ratio of lactide toglycolide is from about 75:25 to about 50:50. In one embodiment, theratio is 50:50.

Illustrative polymers include, but are not limited to,poly(D,L-lactic-co-glycolic acid) (PLGA, 50:50 lactic acid to glycolicacid ratio, M_(n)=10 kDa, referred to as 502H);poly(D,L-lactic-co-glycolic acid) (PLGA, 50:50 lactic acid to glycolicacid ratio, M_(n)=25 kDa, referred to as 503H);poly(D,L-lactic-co-glycolic acid) (PLGA, 50:50 lactic acid to glycolicacid ratio, M_(n)=30 kDa, referred to as 504H);poly(D,L-lactic-co-glycolic acid) (PLGA, 50:50 lactic acid to glycolicacid ratio, M_(n)=35 kDa, referred to as 504); andpoly(D,L-lactic-co-glycolic acid) (PLGA, 75:25 lactic acid to glycolicacid ratio, M_(n)=10 kDa, referred to as 752).

In certain embodiments, the polymer microparticles are biodegradable.

The agent-loaded microparticles may have a volume average diameter of200 nm to 30 μm, more particularly 1 to 10 μm. In certain embodiments,the agent-loaded microparticles do not have a volume average diameter of10 μm or greater since such larger particles are difficult to eject froma container in the form of an eye drop. The agent-loaded microparticlesmay be pore less or they may contain varying amounts of pores of varyingsizes, typically controlled by adding NaCl during the synthesis process.

The agent-loaded microparticle fabrication method can be single ordouble emulsion depending on the desired encapsulated agent solubilityin water, molecular weight of polymer chains used to make themicroparticles (MW can range from ˜1000 Da to over 100,000 Da) whichcontrols the degradation rate of the microparticles and subsequent drugrelease kinetics.

In certain embodiments, the hydrogel may respond to external stimulus(e.g., physiological conditions) such as changes in ion concentration,pH, temperature, glucose, shear stress, or a combination thereof.Illustrative hydrogels include polyacrylamide (e.g.,poly-N-isopropylacrylamide), silicon hydrogels like those used incontact lenses, polyethylene oxide/polypropylene oxide or combinationsof the two (e.g., Pluronics hydrogel or Tectronics hydrogel), butylmethacrylate, polyethylene glycol diacrylate, polyethylene glycol ofvarying molecular weights, polyacrylic acid, poly methacrylic acid, polylactic acid, poly(tetramethyleneether glycol),poly(N,N′-diethylaminoethyl methacrylate), methyl methacrylate, andN,N′-dimethylaminoethylmethacrylate. In certain embodiments, thehydrogel is a thermoresponsive hydrogel.

In certain embodiments, the thermoresponsive hydrogel has a lowercritical solution temperature (LCST) below body temperature. Thethermoresponsive hydrogel remains fluid below physiological temperature(e.g., 37° C. for humans) or at or below room temperature (e.g., 25°C.), solidify (into a hydrogel) at physiological temperature, and arebiocompatible. For example, the thermoresponsive hydrogel may be a clearliquid at a temperature below 34° C. which reversibly solidifies into agelled composition at a temperature above 34° C. Generally, theLCST-based phase transition occurs upon warming in situ as a result ofentropically-driven dehydration of polymer components, leading topolymer collapse. Various naturally derived and synthetic polymersexhibiting this behavior may be utilized. Natural polymers includeelastin-like peptides and polysaccharides derivatives, while notablesynthetic polymers include those based on poly(n-isopropyl acrylamide)(PNIPAAm), poly(N,N-dimethylacrylamide-co-N-phenylacrylamide),poly(glycidylmethacrylate-co-N-isopropylacrylamide), poly(ethyleneoxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), poly(ethyleneglycol)-polyester copolymer, and amphiphilic block copolymers. Thestructure of PNIPAAm, containing both hydrophilic amide bonds andhydrophobic isopropyl groups, leads to a sharp phase transition at theLCST. Studies suggest that the average number of hydrating watermolecules per NIPAAm group falls from 11 to about 2 upon the hydrophobiccollapse above the LCST (32-34° C.). In certain embodiments, theamphiphilic block copolymer comprises a hydrophilic component selectedfrom poly ethylene oxide (PEO), poly vinyl alcohol (PVA), poly glycolicacid (PGA), poly (N-isopropylacrylamide), poly(acrylic acid) (PAA), polyvinyl pyrrolidone (PVP) or mixtures thereof, and a hydrophobic componentselected from polypropylene oxide (PPO), poly (lactic acid) (PLA), poly(lactic acid co glycolic acid) (PLGA), poly (.beta.-benzoyl L-aspartate)(PBLA), poly (.gamma.-benzyl-L-glutamate) (PBLG), poly (aspartic acid),poly (L-lysine), poly(spermine), poly (caprolactone) or mixturesthereof. Examples of such amphiphilic block copolymers include(PEO)(PPO)(PEO) block copolymers (PEO/PPO), and poly (lactic acid coglycolic acid) block copolymers (PLGA), such as (PEO)(PLGA)(PEO) blockcopolymers.

In certain embodiments, the hydrogel is non-biodegradable (e.g.,PNIPAAm). In other embodiments, the hydrogel is biodegradable. Forexample, biodegradable NIPAAm-based polymers can be made by conjugatingthe PNIPAAm with natural biodegradable segments such as MMP-susceptiblepeptide, gelatin, collagen, hyaluronic acid and dextran. Copolymersformed from NIPAAm and monomers with degradable side chains compriseanother category of NIPAAm-based bioabsorbable, thermoresponsivehydrogels. Hydrolytic removal of hydrophobic side chains increases thehydrophilicity of the copolymer, raising the LCST above body temperatureand making the polymer backbone soluble. Due to the relative simplicityof the synthetic process, the most investigated biodegradable monomershave been HEMA-based monomers, such as 2-hydroxyethylmethacrylate-polylactide (HEMA-PLA)(Lee, B. H.; et al. Macromol. Biosci.2005, 5, 629-635; and Guan, J., et al. Biomacromolecules 2008, 9,1283-92), 2-hydroxyethyl methacrylate-polycaprolactone (HEMA-PCL) (Wang,T., et al. Eur. J. Heart Fail 2009, 11, 14-19 and Wu, D., et al. ACSAppl. Mater. Interf. 2009, 2, 312-327) and 2-hydroxyethylmethacrylate-polytrimethylene carbonate (HEMA-PTMC) (Fujimoto, K. L., etal. Biomaterials 2009, 30, 4357-4368 and Wang, F., et al. Acta Biomater.2009, 5, 2901). However, the backbone remnant following hydrolysis,HEMA, presents hydroxyethyl side groups (—CH.sub.2CH.sub.2-OH), whichhave a relatively limited effect on remnant polymer hydrophilicity (Cui,Z., et al. Biomacromolecules 2007, 8, 1280-1286). In previous studies,such hydrogels have been found to be either partially bioabsorbable (Wu,D., et al. ACS Appl. Mater. Interf. 2009, 2, 312-327) or completelybioabsorbable, but have required the inclusion of considerablyhydrophilic co-monomers such as acrylic acid (AAc) in the hydrogelsynthesis (Fujimoto, K. L.; et al. Biomaterials 2009, 30, 4357-4368;Wang, F., et al. Acta Biomater. 2009, 5, 2901; and Guan, J., et al.Biomacromolecules 2008, 9, 1283-92).

In a further embodiment, the thermoresponsive hydrogel degrades anddissolves at physiological conditions in a time-dependent manner. Thecopolymer and its degradation products typically are biocompatible.According to one embodiment, the copolymer consists essentially ofN-isopropylacrylamide (NIPAAm) residues (a residue is a monomerincorporated into a polymer), hydroxyethyl methacrylate (HEMA) residuesand methacrylate-polylactide (MAPLA) macromer residues as disclosed inU.S. Patent Publ. 2012/0156176, which is incorporated herein byreference. Alternately, the copolymer consists essentially ofN-isopropylacrylamide residues, acrylic acid (AAc) residues, andhydroxyethyl methacrylate-poly(trimethylene carbonate) (HEMAPTMC)macromer residues as disclosed in U.S. Patent Publ. 2012/0156176, whichis incorporated herein by reference.

The base precursor (e.g., a prepolymer, oligomer and/or monomer) for thehydrogel, cross linkers, and initiators are mixed together and allowedto polymerize for a predefined period of time (from 1 h to 24 htypically) to form the hydrogel. The hydrogel is then washed to removeany excess initiator or unreacted materials. The hydrogel at this stageis a liquid (e.g., in the form of an aqueous solution) at roomtemperature until it is ready for use. The microparticles can be addedin before, after, or during the polymerization of the hydrogel (addingmicroparticles in before or during polymerization results in a slighterfaster initial drug release rate) to form a suspension of solidmicroparticles in hydrogel. The amount of microparticles loaded into thehydrogel may vary. For example, there may be up to 10 mg, moreparticularly 1 to 5 mg microparticles per microliter hydrogel. Incertain embodiments, the microparticles are homogeneously dispersedwithin the hydrogel. Optional components can be added that allow foreasier visualization of the hydrogel/microparticle suspension such assodium fluorescein or other fluorescent molecules such as FITC,rhodamine, or AlexaFluors or dyes such as titanium dioxide. The watercontent of the swollen hydrogel at room temperature may be 50-80%. Thewater content of the hydrogel after it gels in situ in the eye may be1-10%.

Upon ocular administration of the microparticle/hydrogel liquidsuspension, the microparticle/hydrogel system releases water and canbecome an opaque solid gel member. The gelled member may be sufficientlyfirm that it can be manipulated with tweezers. FIG. 7A depictsadministration of an eye drop 1 comprising the microparticle/hydrogelliquid suspension, gelling of the suspension to form a polymericcrosslinked matrix 2 that encapsulates the agent-loaded microparticles(FIG. 7B), and positioning of the resulting gelled member 3 in the lowerfornix of the eye (FIG. 7C). In one particular embodiment, athermoresponsive hydrogel carrier for the agent-loaded microparticleshas been developed and characterized that will allow patients to apply aliquid suspension (containing the release system) topically to their eyeas they would an aqueous eye drop-based medication (FIG. 7A). When thedrop collects in the conjunctival cul-de-sac, the liquid warms to bodytemperature and thermoresponsive hydrogel de-swells, forming a stable,opaque gel (FIG. 7B). The drop also appears to naturally conform to theshape of the inferior fornix during the gelation (FIG. 7C) promotingretention of the system and continuous delivery of agent to the eye viathe embedded, sustained agent microparticle formulation. Thegel/microparticle system could afford sustained release of an oculardrug for up to 30 times longer than any currently known in situ forminghydrogels. Furthermore, removal of the gelled drop would be as simple asflushing the eye with cold saline, unlike intravitreal orsubconjunctival implants that require removal by a clinician. Thisformulation should lower IOP and increase bioavailability compared totopical eye drops. This new delivery formulation could also serve as amodular platform for local administration of not only a variety ofglaucoma medications (including BT), but a whole host of other oculartherapeutics as well.

The shape of the gelled member 3 may vary and is dependent on theanatomy of the ocular structure. Typically, the gelled member 3 spreadsout into an elongate, thin film of gel, but it may assume a morecylindrical shape. In certain embodiments, the gelled film may have athickness of 10 to 1000, more particularly 100 to 300 μm. The gel can bemanipulated as it undergoes phase transitioning into a desired shape. Incertain embodiments, the gelled member may retain pliability to acertain extent. In certain embodiments, the gelled member 3 may have aresidence time in the lower fornix of at least five days, moreparticularly at least 10 days, and most particularly at least 30 days.

The microparticle/hydrogel system disclosed herein may provide forsustained release of an agent. The agent release can be linear ornon-linear (single or multiple burst release). In certain embodiments,the agent may be released without a burst effect. For example, thesustained release may exhibit a substantially linear rate of release ofthe therapeutic agent in vivo over a period of at least 5 days, moreparticularly at least 10 days, and most particularly at least 30 days.By substantially linear rate of release it is meant that the therapeuticagent is released at a rate that does not vary by more than about 20%over the desired period of time, more usually by not more than about10%. It may be desirable to provide a relatively constant rate ofrelease of the agent from the delivery system over the life of thesystem. For example, it may be desirable for the agent to be released inamounts from 0.1 to 100 μg per day, more particularly 1 to 10 μg perday, for the life of the system. However, the release rate may change toeither increase or decrease depending on the formulation of the polymermicroparticle and/or hydrogel. In certain embodiments, the deliverysystem may release an amount of the therapeutic agent that is effectivein providing a concentration of the therapeutic agent in the eye in arange from 1 ng/ml to 200 μg/ml, more particularly 1 to 5 μg/ml. Thedesired release rate and target drug concentration can vary depending onthe particular therapeutic agent chosen for the drug delivery system,the ocular condition being treated, and the subject's health.

In certain embodiments, the agent release is dependent on degradation ofthe polymer microparticles. As the polymer chains break up, the agentcan diffuse out of the initial polymer microparticle matrix where itwill eventually reach the hydrogel matrix. At that point, the hydrogelmay partially slow down release of the agent but diffusion through thehydrogel is significantly faster than degradation of the polymer. Thusthe limiting factor in agent release is degradation of the polymer.

It is clearly more desirable to demonstrate a method of directlymeasuring the concentrations of release agents diffusing into targettissues directly in vivo for sustained delivery systems. Such atechnology would help researchers ensure that enough drug isadministered to the affected tissues while at the same time minimizingthe risk of potential systemic side effects. Additionally, if acontrolled release system were to be modified (in the future) toincorporate other modalities (such as growth factor-basedneuroprotective agents or antibody-based antiangiogenics), knowledge ofthe amount of drug that reaches posterior tissues could significantlyexpedite the development of such a therapy and provide vastly moreinformation than functional measurements (like IOP) alone.Unfortunately, available methods to detect or visualize in vivo releaseare currently both limited and unwieldy. For example, traditional drugdetection assay methods (such as those using radiolabeled drug) requirelarge numbers of animals for serial sacrifice-type studies to measure invivo drug concentrations in resected tissue. Additionally, the reduceddrug concentrations associated with controlled release can make it evenmore difficult to detect drug in the local microenvironment, let alonein surrounding tissues or systemic circulation.

Accordingly, disclosed herein are embodiments to encapsulate an MRIcontrast agent, e.g., gadolinium-tetraazocyclododecanetetraacetic acid(Gd-DOTA) in the same polymer microparticles as those used to releasethe therapeutic agent and perform in vivo scans over the full treatmentwindow of at least one month, thus representing the use of MRI tovisualize and quantify long-term controlled release in the eye from atopical depot. Rationally-designed, long-term, polymer microparticlebased delivery of Gd-based MRI contrast agents can serve as a reliable,noninvasive method to resolve the spatial and temporal release profileof a variety of therapeutic agents, beginning with BT, from the topicalgel/microparticle formulation described herein. BT and Gd-DOTA have verysimilar molecular weights (approximately 440 and 600 Da, respectively),meaning that degradable release systems that produce practicallyidentical release profiles for both agents can be designed. Furthermore,the ocular half-lives of Gd-DTPA (a contrast agent very similar in sizeand structure to Gd-DOTA) and BT are 28.08 and 28.2 min, respectively,lending further support to the use of Gd-DOTA as a surrogate imagingmarker for BT. Correspondingly, the measurement of local Gd-DOTAconcentrations using MRI may allow tracking of in vivo release behaviorfor both formulations (Gd-DOTA and BT), which can be confirmed (orvalidated) using the traditional, high-sensitivity BT assay detectionmethods. Preliminary ex vivo MRI data for Gd-DOTA-loaded microparticlessuggest that these methods are feasible as a real time, noninvasivequantification method. The unique delivery system described herein wouldallow quantification of Gd-DOTA release from a topical depot, unlikepreviously mentioned studies that were performed using either implantsor injections into the eye. In addition, if future release formulationsare identified that would require sustained delivery of large proteins(>>600 Da Gd-DOTA), it is also now possible to conjugate Gd-DOTA ontothese proteins (not significantly increasing the molecular size of therelease agents) to track their release and distribution into the eye.

The microparticle/hydrogel composition may be administered in the formof a liquid eye drop. The eye drop(s) may be administered to any ocularstructure, but is preferably administered to the lower fornix. The eyedrops may be self-administered by the subject. The eye drop will conformcomfortably to the conjunctival sac and release the loaded agent. Theeye drop may be administered on a regimen wherein the interval betweensuccessive eye drops is greater than at least one day (although incertain embodiments the eye drop may be administered once daily or morethan once daily). For example, there may be an interval of at least 5days, at least one week, or at least one month between administrationsof an eye drop(s). In preferred embodiments, the disclosed eye drops maybe used for sustained monthly delivery of medication as a replacementfor the current clinical standard of once or twice daily eye dropadministration. At the end of the desired administration period, thegelled member can be removed from the eye (for example, via a tweezer orflushing out). In certain embodiments, the hydrogel may be biodegradableso that there is no need to remove the gelled member (this embodimentmay be most useful for treating an acute condition). This systemdisclosed herein not only drastically decreases the dosing frequency(thereby increasing the likelihood of patient compliance andrecovery/prevention of worsening symptoms), it does so while avoidingclinician involvement for administration by being completelynoninvasive.

The microparticle/hydrogel disclosed herein may include an excipientcomponent, such as effective amounts of buffering agents, andantioxidants to protect a drug (the therapeutic agent) from the effectsof ionizing radiation during sterilization. Suitable water solublebuffering agents include, without limitation, alkali and alkaline earthcarbonates, phosphates, bicarbonates, citrates, borates, acetates,succinates and the like, such as sodium phosphate, citrate, borate,acetate, bicarbonate, carbonate and the like. These agents areadvantageously present in amounts sufficient to maintain a pH of thesystem of between about 2 to about 9 and more preferably about 4 toabout 8. As such the buffering agent may be as much as about 5% byweight of the total system. Suitable water soluble preservatives includesodium bisulfite, sodium bisulfate, sodium thiosulfate, ascorbate,benzalkonium chloride, chlorobutanol, thimerosal, phenylmercuricacetate, phenylmercuric borate, phenylmercuric nitrate, parabens,methylparaben, polyvinyl alcohol, benzyl alcohol, phenylethanol and thelike and mixtures thereof. These agents may be present in amounts offrom 0.001 to about 5% by weight and preferably 0.01 to about 2% byweight.

The microparticle/hydrogel system disclosed herein may be useful totreat a variety of ocular conditions, both chronic and acute.Illustrative ocular conditions include: maculopathies/retinaldegeneration: macular degeneration, including age related maculardegeneration (ARMD), such as non-exudative age related maculardegeneration and exudative age related macular degeneration, choroidalneovascularization, retinopathy, including diabetic retinopathy, acuteand chronic macular neuroretinopathy, central serous chorioretinopathy,and macular edema, including cystoid macular edema, and diabetic macularedema. Uveitis/retinitis/choroiditis: acute multifocal placoid pigmentepitheliopathy, Behcet's disease, birdshot retinochoroidopathy,infectious (syphilis, lyme, tuberculosis, toxoplasmosis), uveitis,including intermediate uveitis (pars planitis) and anterior uveitis,multifocal choroiditis, multiple evanescent white dot syndrome (MEWDS),ocular sarcoidosis, posterior scleritis, serpignous choroiditis,subretinal fibrosis, uveitis syndrome, and Vogt-Koyanagi-Haradasyndrome. Vascular diseases/exudative diseases: retinal arterialocclusive disease, central retinal vein occlusion, disseminatedintravascular coagulopathy, branch retinal vein occlusion, hypertensivefundus changes, ocular ischemic syndrome, retinal arterialmicroaneurysms, Coats disease, parafoveal telangiectasis, hemi-retinalvein occlusion, papillophlebitis, central retinal artery occlusion,branch retinal artery occlusion, carotid artery disease (CAD), frostedbranch angitis, sickle cell retinopathy and other hemoglobinopathies,angioid streaks, familial exudative vitreoretinopathy, Eales disease.Traumatic/surgical: sympathetic ophthalmia, uveitic retinal disease,retinal detachment, trauma, laser, PDT, photocoagulation, hypoperfusionduring surgery, radiation retinopathy, bone marrow transplantretinopathy. Proliferative disorders: proliferative vitreal retinopathyand epiretinal membranes, proliferative diabetic retinopathy. Infectiousdisorders: ocular histoplasmosis, ocular toxocariasis, presumed ocularhistoplasmosis syndrome (PONS), endophthalmitis, toxoplasmosis, retinaldiseases associated with HIV infection, choroidal disease associatedwith HIV infection, uveitic disease associated with HIV Infection, viralretinitis, acute retinal necrosis, progressive outer retinal necrosis,fungal retinal diseases, ocular syphilis, ocular tuberculosis, diffuseunilateral subacute neuroretinitis, and myiasis. Genetic disorders:retinitis pigmentosa, systemic disorders with associated retinaldystrophies, congenital stationary night blindness, cone dystrophies,Stargardt's disease and fundus flavimaculatus, Bests disease, patterndystrophy of the retinal pigmented epithelium, X-linked retinoschisis,Sorsby's fundus dystrophy, benign concentric maculopathy, Bietti'scrystalline dystrophy, pseudoxanthoma elasticum. Retinal tears/holes:retinal detachment, macular hole, giant retinal tear. Tumors: retinaldisease associated with tumors, congenital hypertrophy of the RPE,posterior uveal melanoma, choroidal hemangioma, choroidal osteoma,choroidal metastasis, combined hamartoma of the retina and retinalpigmented epithelium, retinoblastoma, vasoproliferative tumors of theocular fundus, retinal astrocytoma, intraocular lymphoid tumors.Miscellaneous: punctate inner choroidopathy, acute posterior multifocalplacoid pigment epitheliopathy, myopic retinal degeneration, acuteretinal pigment epithelitis and the like.

In certain embodiments, the ocular conditions include glaucoma, chronicdry eye, keratitis, post-operative inflammation, conjunctivitis, andbacterial or fungal infections.

Also disclosed herein are methods of controlling IOP in a subject usingthe above-described drug delivery systems. In various embodiments, IOPis maintained at or below about 22 mmHg. The drug may be released suchthat the concentration of the drug is approximately constant over aperiod of at least one day. In other embodiments, the above methodscontrol the IOP for a period of at least 1 day, 2 days, 3 days, or 1week.

Examples Formation of Drug-Loaded Microparticles Summary

BT was encapsulated in poly(lactic-co-glycolic) acid (PLGA)microparticles using a standard double emulsion procedure. In vitro drugrelease from the BT-loaded microparticles was quantified using UV-Visspectroscopy. For in vivo studies, rabbits were randomized to receive asingle subconjunctival injection of blank (no drug) or BT-loadedmicroparticles or twice-daily topical BT 0.2% drops. IOP was monitoredover 28 days along with regular slit lamp examination. Additionally,aqueous humor samples were periodically taken and analyzed for BTconcentration using high-performance liquid chromatography. Followingsacrifice on Day 28, eyes were enucleated and stained for histology. Thedrug loaded microparticles demonstrated a primarily poreless morphologywith a volume average diameter of 7.5±2.9 μm. They released an averageof 2.1±0.37 μg BT/mg particles/day in the in vitro setup. In vivo, thedecrease in IOP was significantly lower in the treated eye for topicalBT versus BT microparticles. In contrast, IOP steadily increased inrabbits injected with the blank microparticles. Additionally, BT levelsin the aqueous humor were maintained below toxic levels throughout thestudy. No evidence of microparticle migration or foreign body responsewas observed in the enucleated eyes following the 28-day study. TheBT-loaded PLGA microparticles deliver over 28 days of BT with a singledose, as confirmed using in vitro release assays. This represents a vastimprovement over the current standard of 56-84 doses. Thesemicroparticles demonstrated effectiveness at reducing IOP in vivo, withno evidence of irritation or infection.

Materials and Methods 2.1 Microparticle (MP) Fabrication

MPs were fabricated using a standard double emulsion procedure (Sanchezet al., 1993; Zweers et al., 2006). Briefly, 200 mg ofpolylactic-co-glycolic) acid (MW 24-38 kDa, viscosity 0.32-0.44 dl/g;Sigma, St. Louis, Mo.) was mixed with 4 ml of dichloromethane (DCM) and12.5 mg of an aqueous brimonidine tartrate solution (Santa CruzBiotechnologies, Santa Cruz, Calif.). The drug/polymer solution wassonicated for 10 s (Sonics VibraCell™) before homogenization in 60 ml 2%poly(vinyl alcohol) (PVA-MW ˜25,000 Da, 98% hydrolyzed, Polysciences)for 1 min at approximately 7000 RPM (Silverson L4RT-A homogenizer). Thisdouble emulsion was then added to 80 ml of 1% PVA and allowed to mix for3 h to evaporate any remaining DCM. MPs were then washed four times bycentrifuging for 5 min at 1000 RPM. The MPs were resuspended in DI waterand placed in a lyophilizer (Virtis Benchtop K freeze dryer, Gardiner,N.Y.) operating at 70 mTorr for 48 hours before being stored at −20° C.

2.2 Microparticle Characterization

The shape and morphology of the MPs was examined using a scanningelectron microscope (SEM). Images were taken on the lyophilized blankand drug-loaded MPs following gold sputter-coating using a JEOL 6335FField Emission SEM (JEOL, Peabody, Mass.). Average particle diameter fora minimum of 10,000 MPs was determined using volume impedancemeasurements on a Multisizer 3 Coulter Counter (Beckman Coulter,Indianapolis, Ind.).

2.3 In Vitro Release Assay

Known masses of lyophilized MPs were suspended in phosphate bufferedsaline (PBS) and incubated at 37° C. MP suspensions were centrifuged for10 min at 1000 RPM after predetermined intervals of time and thesupernatant was removed for analysis. Brimonidine concentration in PBSsamples was measured via UV/Vis absorption using a SoftMax Pro 5microplate reader (Molecular Devices, Sunnyvale, Calif.) at 320 nm. TheMP aliquots were then resuspended in fresh PBS. The results forBT-loaded MPs are reported as the average of three release studies andtheir standard deviation. Any background signal obtained from the blankMPs was subtracted from each measurement.

Theoretical maximum and minimum amounts of BT absorption were alsocalculated as a basis for comparison for in vitro release from theBTMPs. This range was calculated by assuming a 50 μl drop and 2 dropsadministered per day at a rate of either 1% (minimum) or 7% (maximum)absorption (Ghate and Edelhauser, 2008). As the in vitro release methodsmeasure base brimonidine and not the tartrate salt, a necessaryconversion factor of 0.66 mg brimonidine for every 1 mg BT wasincorporated in these calculations (Acheampong et al., 2002).

2.4 In Vivo Studies

Pigmented Dutch belted rabbits were randomized to receive either blankMPs (no drug), BTMPs, or 0.2% BT drops (Alphagan®, Allergan, Irvine,Calif.), with three animals in each group initially. In order to ensurethat statistical significance could be achieved with the minimal numberof animals (as required by IACUC), a sample size analysis was performedwith a power of 0.8 based on previous results comparing IOP measurementsbefore and after topical BT 0.2% administration and insertion of anexperimental ocular insert delivery system in a rabbit model (Aburahmaand Mahmoud, 2011), leading to a n=3 rabbits per group. On day 0, theright eye of rabbits in the blank or drug-loaded MP groups received asuperior subconjunctival injection of 5 mg of MPs suspended in 0.050 ccsterile saline. Rabbits in the BT drops group received a single drop of0.2% BT solution in one eye twice a day for every day of the study. Theleft eye remained untreated in all animals throughout the study.

Samples of venous blood and aqueous humor were taken on Days 0 (prior toadministration of treatment), 1, 3, 7, 14, 21, and 28. These sampleswere stored at −20° C. prior until assaying for brimonidineconcentration assay using high performance liquid chromatography (HPLC,see below). Eyes were regularly checked for signs of infection orirritation by instilling sodium fluorescein drops in each eye andexamining with a portable slit lamp containing a cobalt blue light(Reichert Technologies, Depew, N.Y.). IOP was also measured in both eyesusing a Model 30 Classic pneumatonometer (Reichert Technologies, Depew,N.Y.). Tonometry was always performed between the hours of 8 am and 11am and immediately at the induction of intravenous anesthesia with a1:10 mix of xylazine and ketamine Approximately 0.09 ml of anestheticwas required.

Animals were sacrificed on Day 28, and both treated and untreated eyeswere enucleated for histological analysis. The eyes were embedded inparaffin prior to sectioning and staining with hematoxylin and eosin,periodic acid-Schiff (PAS), or Masson's trichrome stain. All slides wereanalyzed for any evidence of intra- or extra-ocular abnormalities by amasked examiner.

2.5 HPLC Analysis

Methods for analyzing brimonidine content in aqueous humor and plasmawere adapted from those in Karamanos et al. (1999) (Karamanos et al.,1999). Samples were analyzed using an UltiMate 3000 HPLC system (Dionex,Sunnyvale, Calif.) to ensure that toxic levels of drug were notdetectable either locally or systemically. Briefly, approximately 20 μlsamples were taken for reverse-phase, isocratic HPLC analysis. ASupelcosil LC-18 column (Sigma Aldrich) was used with 10% (v/v)acetonitrile in TEA buffer as the mobile phase. The separation wasperformed at room temperature at a flow rate of 1.0 ml/min. Retentiontime was approximately 5-10 min and brimonidine was detected at awavelength of 248 nm.

2.6 Statistical Analysis

One-way analysis of variance (ANOVA) was performed on baseline IOPmeasurements to ensure that the three groups could be considered samplesfrom a single population. Subsequently, ΔIOP was calculated at each timepoint, defined as the group-specific change in average IOP from Day 0.ΔIOP at each time point for the BTMP group was compared to the positivecontrol topical BT drops group using a two tailed, two-sample student'st-test with a significance criterion of 5%. This calculation requires 3samples and therefore could not be performed against the blank MPnegative control group due to an anesthesia-related complication in oneanimal in this group early in the study.

3. Results 3.1 Microparticles

To test the hypotheses, a controlled release system capable of 1 monthof brimonidine tartrate (BT) administration was required. As describedabove, this anti-glaucoma medication was encapsulated in degradable PLGAmicroparticles (MPs) successfully using a double emulsion technique. Apreliminary in vitro characterization of the MPs was performed toconfirm their suitability for use in a subconjunctival injection modelprior to beginning assays of drug release. Although a formulation's invitro release behavior is not ipso facto analogous to how release wouldproceed in vivo, it can indeed be indicative of either local or topicalrelease scenarios and is, regardless, an important part of the overallcharacterization of a new, prototype formulation.

FIG. 1 shows scanning electron microscope (SEM) images of thebrimonidine tartrate-loaded MPs (BTMPs). These images confirm that asmooth surface and uniform shape were achieved according to our designspecifications. These images also agree with volume impedancemeasurements, which determined the volume average diameter of the BTMPsto be 7.46±2.86 μm. This size distribution is as expected for theconditions used to fabricate the BTMPs. Ultimately, these MPs are smallenough to be easily injected with a 30-gauge needle while still beinglarge enough to avoid phagocytic removal or migration from the site ofinjection (Shanbhag et al., 1994).

Having confirmed that the size and surface characteristics of the BTMPswere suitable for use in the rabbit model, the next step in the rationaldesign process was to determine the 28-day release profile of drug fromthe MPs. Accordingly, in vitro release of BT from a known mass of theseparticles for over one month is represented in FIG. 2. As the goal wasto release an amount of drug comparable to standard eye drop medication,the amount released as a concentration instead of percentage of totalamount of drug encapsulated is reported. Also shown in FIG. 2 are thetheoretical minimum and maximum amounts of topical BT 0.2% solutionabsorbed into the anterior chamber, as described in the methods section.As expected, the amount of BT released for the full month was within theupper and lower limits for absorption of topical BT 0.2%, with anaverage of 2.1±0.37 μg brimonidine/day released over 28 days. Thisaverage amount includes days 24-28, at which point release ofbrimonidine had slowed considerably.

3.2 Animal Studies

Once the BTMP formulation was proven to release the drug locallyaccording to design specifications, the ability of this released BT (intreated animals) to reduce IOP in a rabbit model over a 30-day timeframe was tested. Approximately 5 mg in 0.05 ml of blank or drug-loadedMPs was injected into the superior subconjunctival space of pigmentedDutch belted rabbits on a 30 gauge needle (n=3 for each group initially;however, one rabbit in the blank MP group was removed from the study dueto an adverse reaction to anesthesia unrelated to the MP injection orsurgical manipulations). Blank MPs were used as the negative control asan indication of IOP in the absence of BT as well as the effect, if anyof the PLGA microparticles on IOP and inflammation. FIG. 3 shows anexample of the MP bleb in the subconjunctival space in one animal on Day1 of the study. A third set of rabbits received twice-daily topical BT0.2% drops at the same time each day to serve as the positive control.

The IOP was measured over 28 days by an ophthalmologist trained inpneumatonometry. For each measurement, the pneumatonometer result has alow standard deviation, generally <0.4 mm Hg. Initially, a baseline IOPmeasurement was taken on each rabbit before beginning treatment.Following administration of drug or MPs (blank or BT-loaded), IOPmeasurements were taken at the same time of day for each time point inthe study, just before eye drops were administered to the positivecontrol group. FIGS. 4a and 4b demonstrate the actual IOP valuesrecorded at each time point for all three groups (blank MPs, topical BTdrops, and BTMPs) in the right eye and left eye, respectively. IOPvalues are reported as the average IOP and standard deviation for thethree animals in each group.

To better understand the changes in IOP over course of the study, therelative differences in IOP compared to each of the baseline values wascalculated. FIGS. 5a and 5b depict the change in IOP at each time pointcompared to day 0 for all three groups, again in the right eye and lefteye, respectively. IOPs recorded on Day 0 were not significantlydifferent between animals in the blank MP, BTMP, and topical BT groupsby one-way ANOVA. IOP reduction was significantly greater (p<0.05) inthe BTMP group compared to the topical BT group for every time point inthe right but not the left eye. While there was no sign of IOP reductionin the blank MP group, statistical analysis could not be performed forthose animals after Day 0 due to the reduced sample size.

In addition to determining the efficacy of the BTMPs in vivo, the safetyand compatibility of the PLGA MPs in the local environment throughoutthe 28-day study was investigated. Brimonidine was not detected ineither the aqueous humor or plasma using an extremely sensitive HPLCmethod. Although this is expected for therapeutic levels (0.53-3.7ug/day according to the calculations in Section 2.3), which implies thatthe amount released was below the detection limit of even HPLC, thisdoes indeed suggest that higher, toxic levels of BT are not produced. Asan additional measure of the safety of the BTMPs, the cornea,conjunctiva, anterior chamber, and periocular tissues were inspectedusing a portable slit lamp throughout the study for signs ofinflammation. The only evidence of inflammation appeared to be relatedto surgical manipulations performed as part of the study, resulting iniridocorneal focal adhesions in the first week for all animals in thestudy. The location of these adhesions was consistent with iris pluggingthe 30 gauge needle paracentesis tracks that were used to collectaqueous samples. This inflammation was cleared prior to Day 14 of thestudy. Eyes were enucleated and stained using H&E, PAS, and Masson'strichrome for histological analysis following sacrifice of the rabbitson Day 28. The resulting slides revealed minimal amounts of fibroustissue surrounding the area of injection (1-2 cell layers thick). Noacute or chronic inflammation suggestive of a foreign body response orinfection was present. Additionally, none of the histology evaluatedshowed any evidence of particle migration from the original injectionsite. The partially degraded MPs in the subconjunctival space can beseen in FIG. 6. Similar images for the remaining rabbits that receivedeither blank or drug-loaded MPs showed that the tissue surrounding theMPs appeared normal.

Hydrogel/Microparticle Suspensions

The microparticles are added to the liquid hydrogel after it has beenthoroughly washed and gently mixed to homogeneously suspend them.Incubation times of approximately 20-30 minutes are ideal for adequatesuspension of particles. Typically we suspend 10-50 mg of particles inapproximately 50 ul of gel solution.

The thermoresponsive gel developed for ocular delivery as describedherein was tuned to have a phase transition temperature below 37° C.with sufficient crosslinking density to reversibly form an opaque gel.In this embodiment, the pNIPAAm-based gel transitions from a liquid to agel over approximately 5 seconds at 34° C. In addition, thethermoreversible gels were designed to be non-degradable, as confirmedby dehydrating and weighing gel/microparticle samples in conjunctionwith the release study. Initial cytotoxicity testing of the gel/particlesuspension on Chang conjunctival cell line (ATCC) showed no deleteriouseffects in vitro with a minimum of 5 washes, necessary to remove theinitiating agents used during polymerization of the gel. Thecustom-designed BT release microparticles effectively provide releaseover one month as well when suspended in the gel as they do in freesolution (see FIG. 8). In other words, the incorporation of theengineered microparticles into the gel does not significantly impact theintended release profile of BT from the system.

The microparticle/hydrogel suspensions can be administered to a rabbitto test whether the gelled member can remain in the lower fornix for aminimum of 30 days, whether or not the gelled member results ininflammation, and the ability of gelled member to reduce intraocularpressure in rabbits that have ocular hypertension (an experimental modelof glaucoma). The microparticle/hydrogel suspensions also can be loadedwith a gadolinium based contrast agent for magnetic resonance imaging toquantify the amount of contrast agent reaching different areas of theeye such as the cornea, retina, optic nerve, and systemic circulation.This will provide information about the usefulness of this system fordelivering drugs for diseases other than glaucoma such as age-relatedmacular degeneration and macular edema.

The effectiveness of the gelling eye drop formulation may be tested in aconventional, serial sacrifice-type study using a rabbit model ofchronic glaucoma adapted from similar methods using non-human primates.New Zealand white rabbits may be used for this study because their eyesare similar in size to human eyes. To induce ocular hypertension, a 50μl volume of 20 μm latex beads may be injected into the anteriorchamber, which has been shown to result in increased IOP for up to 5weeks, with a maximum of nearly twice the baseline IOP. To achieveincreased IOP for the full study, we will inject the microbeads twotimes 5-6 weeks apart and IOP increase will be validated first incontrol animals. This model has also been shown to cause RGC axon death,making it a suitable model for determining the neuroprotective effect,if any, of our treatment method. Following confirmed induction of ocularhypertension, the rabbits will have one eye randomized to receive one ofthree therapies: BT solution 2 times a day (positive control), vehicleonly delivery system of gel containing BT-free microparticles (negativecontrol), and the BT-loaded microparticle/hydrogel drop. IOP will bemeasured using both pneumatonometry and rebound tonometry (using theTonoVet® handheld tonometer) several days before beginning treatment toestablish a baseline. IOP measurements will be taken a minimum of threetimes per week from the onset of therapy until the end of the study,lasting up to three months. Aqueous samples will be drawn periodicallyfrom the anterior chamber on those days to measure levels of drug in theeye, and blood samples will be taken from the marginal ear vein tomeasure systemic concentrations of the drug. As systemic BTconcentrations will likely be quite low, we will use establishedpurification methods and high-performance liquid chromatography (HPLC)to perform these assays. The main outcome measures will be 1) reductionin IOP, 2) mean aqueous levels of drug, and 3) systemic concentration ofthe drug in blood samples. It is expected that the experimental deliverysystem tested in this study will demonstrate comparable (or better) IOPreduction and aqueous BT concentration when compared to the positivecontrol group with a significantly lower systemic drug concentration.Slit lamp examination will also be used to evaluate for condition of theeyes prior to and during therapy to evaluate for any evidence of sideeffects.

Upon completion of the in vivo study, all eyes will be enucleated andprepared for histological analysis using paraffin embedding and stainingtechniques. The overall health and appearance of tissue surrounding theeye drop (cornea, sclera, conjunctiva, and eyelid) will be examined aswell as other tissues of interest, particularly the retina and opticnerve to determine the in vivo toxicity after long-term exposure. Morespecifically, we will determine if any appreciable retinal ganglion cell(RGC) axon loss has occurred using common histopathological techniques.Any potential areas of damage will be identified using light microscopyand image analysis software (ImageJ, NIH) will be used to count thenumber of axons in each damage area for comparison between treated andcontrol eyes.

The following groups and animal numbers, based on a power analysis ofour preliminary in vivo IOP data, will be used to demonstratestatistically significant IOP reduction at each time point in our invivo studies:

Group description Number of Rabbits BT 0.15% drops twice daily 5 Gel andmicroparticles containing no drug 5 Gel and BT-loaded microparticles 5Total per time point 15

Although we have already seen success using both the microparticles andthe hydrogel in vivo, it is possible that we will have issues withretention of the eye drop in some of the rabbits over one month. Forinstance, the presence of the nictitating membrane in rabbits may causethe drop to become dislodged over time, which, although not a concernfor human patients, would affect the efficacy testing. In our initialwork, we have been able to improve retention of the gel/microparticledrops by incorporating a mucoadhesive, water-soluble form of chitosaninto the gel. Should retention still prove to be an issue at later timepoints (particularly in the three month formulation), a variety ofminimally invasive options exist to mitigate this effect, includingsuturing of the gelled drop to the lower fornix, amputation of thenictitating membrane, or a one-time injection of botulinum toxin (suchas Botox®, commonly used to treat strabismus in adults) to temporarilyreduce functionality of the nictitating membrane. Another potentialissue may be insufficient or inconsistent IOP increase in the rabbitsreceiving the microbead injection and a resultant lack of effect oftreatment. Two types of tonometry will be used to ensure accuratemeasurements but if the initial validation of our in vivo glaucoma modeldoes not show an adequate increase in IOP (defined as significantlyhigher IOP compared to baseline for at least 4 weeks), we willincorporate a third between the microbead injections at the beginningand midpoint of the study. In our experience and in independent studiesof the microbead occlusion model in rodents, multiple injections havebeen shown to produce a consistent, longer duration of IOP increase.Thus we anticipate that using these techniques and a thorough initialvalidation would adequately address insufficiencies with ourexperimental model.

In Vivo Testing of Hydrogel/Microparticle Suspensions

The gel/microparticle drop was tested in a rabbit model over 28 days.The nictitating membrane (third eyelid) was resected prior toadministering the drop in order to better represent retention in a humaneye (see FIG. 11). The drop was administered with no prior restraint,sedation, or local anesthesia necessary (FIG. 12A). The findings were asfollows:

The drops resulted in no irritation or infection in any of the rabbits,as evaluated using slit lamp examination. The drops were identifiedintact through 21 days, at which time the appearance of thegel/microparticle seemed to indicate that it had broken into smallerpieces (or that the drop had partially fallen out of or migrated awayfrom the inferior fornix). FIG. 13 shows the gel/microparticle drops atvarious time points. The presence of the gels was confirmed usingfluorescein staining and cobalt blue light, which differentiates the gelfrom surrounding tissues by giving it a bright green color.

Regardless of the appearance of the gels, the data suggest once againthat intraocular pressure relative to the negative control group wassignificantly lower at every time points but one (presumably due toabnormally low pressure in the negative control group on that day, asseen in FIG. 14A). These results correspond well with those seen withboth the microparticles alone and the positive control (topical eyedropmedication), with the exception that both experimental treatmentsactually outperformed the drops at the time of measurement on Day 14.

In the control eye, little to no effect on intraocular pressure wasobserved. This once again suggests that the experimental treatment had amarkedly decreased systemic uptake compared to the traditional eyedropmedication group (FIG. 14B).

In Vitro Testing of Gd-DOTA Microparticles

We utilized the release behavior of BT (FIGS. 2 and 8) to generatedesign specifications and build the custom Gd-DOTA formulation. Toconfirm that the specifications for release behavior were met in the newGd-DOTA formulation, we incubated a known mass of this formulation in abuffer solution and measured Gd-DOTA release over time using both MRIscans at predefined time points and also time-resolved fluorescencemeasurements (as a secondary method to confirm Gd-DOTA concentration).Although the data shown in FIG. 9 suggests that some minor formulationtuning may be required, the behavior of our preliminary Gd-DOTAformulation already corresponds extremely well with that of the BTrelease formulation, increasing the likelihood of successfully achievingour proposed aims. Similarly, these results further demonstrate thereliability of our in silico methods for preparing these type of releaseformulations. Overall loading of Gd-DOTA was also measured usinginductively-coupled plasma mass spectrometry (ICP-MS) (and confirmedusing the TRF spectrophotometric method) and determined to be 5.6 ug/mgmicroparticles. These loading results agree with those of Doiron et al.(2008) for 5 h release of Gd-DTPA, an alternative contrast agent withsimilar size and structure to Gd-DOTA, entrapped in PLGA microspheres.

To demonstrate the feasibility of quantifying local controlled releasefrom a gel/microparticle depot using MRI, we performed post-mortemT1-weighted MRI scans of New Zealand White rabbits at 24 h followingintravitreal injection (in the right eye only) of the Gd-DOTA loaded MPdepot (FIG. 10a ) and soluble Gd-DOTA (FIG. 10b ), both contained withinthe thermoresponsive hydrogel matrix. Scans were performed within onehour of sacrifice. Soluble Gd-DOTA without MP encapsulation was largelycleared from the injection site at 24 h, with only 56% and 59% signalintensity (relative to nearby muscle tissue) in the vitreous andanterior chamber, respectively. In contrast, the controlled releaseGd-DOTA loaded MPs generated a 690% and 347% larger signal intensityrelative to that of muscle in the vitreous and anterior chamber,respectively (FIG. 10a ). These results demonstrate our ability to trackrelease and clearance of Gd-DOTA in the eye in whole brain scans as wellas the slower release of Gd as indicated by the significant increase insignal intensity at 24 h in the Gd-DOTA loaded gel/MP depot. Thisplacement allowed us to show that these agents could be located in wholeanimal scans and the corresponding release of Gd-DOTA can be quantifiedin various ocular tissues. We anticipate that, similar to ourpost-mortem results, the proposed in vivo studies will demonstrate acontrolled release pattern from the gel/microparticle depot into thelocal environment analogous to the in vitro release data in FIG. 9. Thespatiotemporal distribution of Gd-DOTA into the rest of the eye willalso provide valuable data for future controlled release formulations ofother ocular therapeutics, such as those targeting the posterior segmentof the eye.

We will develop at least two Gd-DOTA-loaded microparticle formulationsfollowing a one-month release schedule (analogous to the currentBT-loaded microparticle formulation) and also a three-month releaseschedule (analogous to the proposed BT-loaded microparticleformulation). Though the current Gd-DOTA microparticle formulationalready shows good agreement for the former release schedule in vitro,we will make adjustments to pore size and particle size to diminish theinitial burst seen in the first three days to achieve a better match tothe one-month BT release. We will use MRI and spectrophotometry todetect the in vitro release of Gd-DOTA from the microparticles. Loadingefficiencies will again be determined using TRF and confirmed withICP-MS and the surface morphology and size of the particles will bedetermined in vitro prior to their use in vivo.

The candidate Gd-DOTA-loaded microparticles identified during in vitrotesting will be tested in a healthy rabbit model, similarly to theBT-loaded, gelling eye drops. Administration of the gelling eye dropscontaining contrast agent will be done in the same way as with thedrug-loaded version, in contrast to the preliminary studies in which MPswere injected intravitreally. We will scan the rabbits at various timepoints using high-resolution T1 mapping techniques in a 3T MRI scannerat the Neuroscience Imaging Center at the University of Pittsburghthroughout the study (lasting a maximum of three months) to determinethe location and concentration of released contrast agent. Theconcentration of contrast agent in various ocular components, forexample the anterior chamber and the vitreous, will be compared to BTconcentration in those same tissues. Thus, we will be able to determinehow well concentration of BT in various compartments of the eye followsconcentration of contrast agent. The measure of success of theseexperiments will be release of Gd-DOTA to the local area of thegel/microparticle depot that matches concentration of BT in the sameareas (as determined by aqueous samples taken from rabbits in the serialsacrifice study). Following completion of the in vivo MRI studies, wewill once again perform slit lamp examination and tonometry measurementsto evaluate the ocular health of the rabbits. We will also periodicallytake samples of aqueous humor and vitreous humor as well as venous bloodsamples from the marginal ear vein as a secondary confirmation of localand systemic contrast agent release. MRI and spectrophotometric Gd-DOTAconcentration data will be compared to in vivo BT concentration data.Upon concluding the in vivo studies, eyes will be enucleated andevaluated for their overall appearance and health using commonhistopathological analysis techniques.

Three Month Release

This embodiment describes a formulation “recipe” that would be suitablefor sustained, linear release of BT for a three-month period. Morespecifically, 90 days of linear release of BT may be realized using thefollowing fabrication parameters: 1) Rp (overall particle radius)=10 μm,2) Rocc (inner occlusion or pore size)=0.03 μm, 3) Mwd=256 kDa, 4) kCw(degradation rate constant)=1.00E-6 days⁻¹, and 5) a ratio ofapproximately 2% low MW, 27% middle MW, and 71% high MWpoly(lactic-co-glycolic acid) (PLGA) containing 50% each of lactide andglycolide monomers. Microparticles will be fabricated using a standarddouble emulsion procedure from an organic solution of PLGA (areadily-translatable, biocompatible and biodegradable polymer) that ismicro-emulsified along with an aqueous BT solution. The in vitro releaseof BT over three months will be tested by incubating a known mass ofmicroparticles in a buffer solution at 37° C. Samples will be taken atregular intervals and buffer will be replaced to maintain sink-likeconditions. The buffer samples containing BT will be assayed for BTconcentration using spectrophotometric absorbance at a wavelength of 320nm.

Modifying Phase Transition Properties of the Gel

Cross-linking density and concentration of other reagents play key rolesin determining the phase transition time and temperature of the gel. Theaddition of poly(ethylene glycol) PEG (400 Da) enables the drop to beopaque (and therefore easily visible with the naked eye) and firm enoughto be removed with tweezers. We can further tune the amount of PEG addedand the molecular weight of PEG to lower the phase transitiontemperature closer to an ideal value of 27° C. (as low as possible whilestill being sufficiently above room temperature). The maximum loading ofmicroparticles in drops will be determined by performing stabilitytesting of the gelling drops in vitro. The gel/microparticle sampleswill be weighed at varying time points to ensure that, as with theoriginal gel formulation, degradation of the drop is negligible over thetimeframe of delivery.

Hydrogel/Microparticles with Other Drugs

The loading and release of other drugs (moxiflxacin and vancomycin) withthe microparticles embedded within the gel has also been confirmed. Thisdata indicates the use of this therapy for other ocular diseases (inthis case, to treat ocular infection or for prophylactic use followingocular surgery).

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention.

What is claimed is:
 1. A composition comprising agent-loaded polymermicroparticles dispersed within a thermoresponsive hydrogel, wherein theagent is an agent for treating an ocular condition and the compositionis configured for sustained topical ocular release of the agent.
 2. Thecomposition of claim 1, wherein the composition is a liquid that can beadministered to a subject in the form of an eye drop.
 3. The compositionof claim 1, wherein the agent is an agent that lowers intraocularpressure, the microparticles are biodegradable, and the hydrogel is notbiodegradable.
 4. The composition of claim 1, wherein the agent-loadedpolymer microparticles have a volume average diameter of 1 to 10 μm. 5.A drug depot positioned in the lower fornix of an eye of a subject,wherein the drug depot comprises a gelled hydrogel comprisingdrug-loaded polymer microparticles.
 6. The drug depot of claim 5,wherein the drug depot is removable by the subject after a residencetime in the lower fornix of at least five days.
 7. The drug depot ofclaim 5, wherein the drug depot is removable by the subject after aresidence time in the lower fornix of at least thirty days.
 8. The drugdepot of claim 5, wherein the agent is an agent that lowers intraocularpressure, and the microparticles are biodegradable.
 9. The drug depot ofclaim 5, wherein the hydrogel comprises poly(n-isopropyl acrylamide).